1. Field of the Invention
The invention relates to a vehicle position recognition system that includes a vehicle position calculation unit that calculates an estimated position of a vehicle based on satellite positioning and dead reckoning navigation, and an error range calculation unit that calculates an error range based on the estimated position, taking into account an error in the estimated position.
2. Description of the Related Art
The above-described vehicle position recognition system, which includes the vehicle position calculation unit and the error range calculation unit, is used for calculating a vehicle position in a car navigation apparatus. Japanese Patent Application Publication No. 2005-249654 (JP-A-2005-249654) (paragraphs 0006 to 0009 and 0040, FIG. 1, and FIG. 5) describes a navigation apparatus that determines a vehicle position using satellite positioning, and determines the vehicle position using dead reckoning navigation, as an example of related art. In the navigation apparatus described in the publication No. 2005-249654, a longitudinal slope of a road on which a vehicle is traveling is calculated as an actually-measured slope, based on a change in an altitude measured using the satellite positioning, and the road on which the vehicle is currently traveling is determined as a vehicle traveling road, based on map data that indicates a road map. In the navigation apparatus, further, the reliability degree of the position determined using the satellite positioning is calculated based on the longitudinal slope of each road, or based on the degree of deviation of the actually-measured slope from a range of the longitudinal slope. The radius of a circle indicating an error range is changed according to the degree of reliability. More specifically, the radius of the circle indicating the error range is increased with a decrease in the degree of reliability.
Japanese Patent Application Publication No. 11-37776 (JP-A-11-37776) (paragraphs 0008 to 0014, FIG. 3, and FIG. 4) describes a navigation apparatus for a vehicle as another example of related art. In the navigation apparatus described in the publication No. 11-37776, a travel error range is obtained based on a vehicle traveling position calculated using signals from vehicle-mounted sensors, and an error of accuracy in the calculated vehicle traveling position. A differential GPS (DGPS) error range is obtained based on the vehicle position determined using the DGPS and the error of accuracy in the obtained vehicle position. A more limited vehicle existing range is set based on the travel error range and the DGPS error range. The vehicle position on a road is estimated based on the vehicle existing range and road map information. Further, in the navigation apparatus for a vehicle, the vehicle existing range is set to a range where the travel error range and the DGPS error range overlap with each other, or one of the travel error range and the DGPS error range, which is smaller than the other. Thus, the small and accurate vehicle existing range is set.